// Copyright 2017 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// PLEASE READ BEFORE CHANGING THIS FILE!
//
// This file implements the out of bounds trap handler for
// WebAssembly. Trap handlers are notoriously difficult to get
// right, and getting it wrong can lead to security
// vulnerabilities. In order to minimize this risk, here are some
// rules to follow.
//
// 1. Do not introduce any new external dependencies. This file needs
//    to be self contained so it is easy to audit everything that a
//    trap handler might do.
//
// 2. Any changes must be reviewed by someone from the crash reporting
//    or security team. See OWNERS for suggested reviewers.
//
// For more information, see https://goo.gl/yMeyUY.
//
// This file contains most of the code that actually runs in a trap handler
// context. Some additional code is used both inside and outside the trap
// handler. This code can be found in handler-shared.cc.

#include "src/trap-handler/trap-handler-internal.h"
#include "src/trap-handler/trap-handler.h"

namespace v8 {
namespace internal {
    namespace trap_handler {

#if V8_TRAP_HANDLER_SUPPORTED

        // This function contains the platform independent portions of fault
        // classification.
        bool TryFindLandingPad(uintptr_t fault_addr, uintptr_t* landing_pad)
        {
            // TODO(eholk): broad code range check

            // Taking locks in the trap handler is risky because a fault in the trap
            // handler itself could lead to a deadlock when attempting to acquire the
            // lock again. We guard against this case with g_thread_in_wasm_code. The
            // lock may only be taken when not executing Wasm code (an assert in
            // MetadataLock's constructor ensures this). The trap handler will bail
            // out before trying to take the lock if g_thread_in_wasm_code is not set.
            MetadataLock lock_holder;

            for (size_t i = 0; i < gNumCodeObjects; ++i) {
                const CodeProtectionInfo* data = gCodeObjects[i].code_info;
                if (data == nullptr) {
                    continue;
                }
                const Address base = data->base;

                if (fault_addr >= base && fault_addr < base + data->size) {
                    // Hurray, we found the code object. Check for protected addresses.
                    const ptrdiff_t offset = fault_addr - base;

                    for (unsigned i = 0; i < data->num_protected_instructions; ++i) {
                        if (data->instructions[i].instr_offset == offset) {
                            // Hurray again, we found the actual instruction.
                            *landing_pad = data->instructions[i].landing_offset + base;

                            gRecoveredTrapCount.store(
                                gRecoveredTrapCount.load(std::memory_order_relaxed) + 1,
                                std::memory_order_relaxed);

                            return true;
                        }
                    }
                }
            }
            return false;
        }
#endif // V8_TRAP_HANDLER_SUPPORTED

    } // namespace trap_handler
} // namespace internal
} // namespace v8
